Idiopathic pulmonary fibrosis was ruled out on the basis of the criteria of the American Thoracic Society. The criteria stipulate that a diagnosis of idiopathic pulmonary fibrosis cannot be entertained when there is occupational history of exposure to agents potentially toxic and fibrogenic to the lung. Whereas a transthoracic lung biopsy would have been more precise, we could rule out other causes for pulmonary fibrosis and, together with the strong occupational exposure to ammonia gas, support the diagnosis of interstitial lung fibrosis as a result of repetitive ammonia inhalation.